Many commonly used chemicals are produced and sold in pulverulent form but are then slurried, dispersed, or dissolved in water when used by the consumer. Examples of these materials are pesticides, specifically insecticides, herbicides, nematicides, and fungicides, and the like, which are applied as a water spray; cleaning products, such as laundary detergents, bleaches, and caustic cleaners, which are dissolved in wash water; process chemicals, such as carbon black and activated charcoal, which can be slurried in water; and pigments and dyes which are dissolved or dispersed.
The films of the invention eliminate problems associated with the use of these pulverulent types of products. One such type of problem involves exposure of the user to the chemical, or chemicals, of which such products are composed. Opening a package of finely ground material, measuring an amount of the material, and transferring the measured amount from the package to equipment in which the material is contacted with water can generate air-borne dust with which the user may undesirably come in contact. Thus, a pesticide dust may be irritating to the eyes or mucous membranes of the nose or throat of the user. Such air-borne dust can also contaminate the area in which it is generated. For example, an herbicide dust could damage plants in the area in which the packages are opened, and pigment or activated charcoal dusts present extremely difficult clean-up problems.
Another type of problem which may be encountered in using common pulverulent chemicals relates to accuracy of measurement thereof. It is frequently extremely difficult to accurately measure materials which have become compacted and/or lumpy, or to transfer powdery materials in the areas exposed to wind. The use of too much or too little of an active ingredient is undesirable. In any event, the former is wasteful, and it can also be harmful; e.g. the use of too much of a pesticide can cause damage to desired plants. The use of too little of an active ingredient can make it partially or totally ineffective.
Moreover, after a chemical has been used, the user is faced with the problems of disposing of the package in which the chemical was delivered. It may contain residual amounts of a material which presents a pollution problem, or is potentially hazardous to humans, harmful to plants or animals, or merely unpleasant or unsightly.
Currently available water-soluble films and packages possess one or more of a variety of deficiencies. None of the currently available polymeric compositions based on polyvinyl alcohol can be used to prepare films having the following properties in combination: rapid cold water-solubility; melt-extrudability; good low-temperature package drop strength; and ease of use in automatic packaging techniques, including good heat-sealability and ease of tracking. Many films, which are characterized as water-soluble, dissolve slowly or dissolve incompletely in cold water, resulting in the formation of gel-like particles. These particles tend to deposit on vessel walls, piping, pumps, and valves, and restrict or prevent flow through screens and nozzles.
Many of the currently available compositions utilized in the preparation of such films possess physical properties which require the use of large, expensive, technologically complex film-making equipment, the operation of which consumes large amounts of energy, e.g., solvent-casting (or doctor knife, belt-casting or band casting). Preferable to such preparation methods is melt extrusion. Melt-extrusion process equipment, when compared to the equipment used in water casting, is extremely small, inexpensive, technologically simple, and consumes very little energy. However, there are few polymeric compositions known which are sufficiently water-soluble so as to be suitable, and those that may be sufficiently water-soluble are not sufficiently melt-extrudable to be suitable.
Many water-soluble films of the prior art possess physical properties which make the film unsuitable for use in packaging quantities of pulverulent materials in the range of one hundred grams to ten kilograms (e.g., low temperature package drop strength, yield strength, tear resistance, toughness, flexibility). Such films are also undesirable for the use in automatic packaging machinery. The constituents of many of the water-soluble packaging films currently available are, in general, difficult to obtain or expensive.
Tsuchiya et al., in Japanese publication No. 28,588/69 disclose that water-soluble films can be made by melt-extrusion from 100 parts of a polyvinyl alcohol having a solution viscosity of 18 cps .+-.2 and a degree of saponification of 86.5-89 mol percent, and 10-43 parts of ethylene glycol as a plasticizer. Tsuchiya et al. also list glycerin, triethylene glycol, and other glycols, such as polyethylene glycol, as possible plasticizers; however, no polyethylene glycol is particularly identified (such as by molecular weight); and no data are given for the use of any plastizizer other than ethylene glycol. Moreover, Tsuchiya et al. state that when the die or resin melt temperature is 140.degree. C. or less, it is impossible to extrude the material as a film, and that at temperatures of 185.degree. C. and higher, unsatisfactory film was obtained.
Takigawa et al., in U.S. Pat. No. 3,607,812, describe melt-extrusion of polyvinyl alcohol film which is insoluble in water at a temperature below 40.degree. C. from 87-95 parts by weight polyvinyl alcohol having a degree of polymerization between 700 and 1,500 and a degree of hydrolysis of at least 97 mol percent, which polyvinyl alcohol is combined with 13 to 5 parts by weight of a polyhydric alcohol plasticizer, such as polyethylene glycol having a molecular weight of approximately 200.
Monaghan et al., in U.S. Pat. No. 3,365,413 disclose preparation of polyvinyl alcohol film by a blow-extrusion process with the object of preparing a completely clear film which is soluble in water; no cold water-solubility is disclosed. Although their film was made by blow-extrusion, in preparing packages therefrom, they used an aqueous-sealing technique rather than the more convenient heat-sealing technique which is conventionally used with thermoplastic films. Monaghan et al. indicate that a composition suitable for this purpose must satisfy certain requirements as to the type of polyvinyl alcohol used, and as to the plasticizer that is used. They specify in general that the polyvinyl alcohol be hydrolyzed so as to contain between 60 and 75% of hydroxyl groups and 40 to 25% of residual ester groups. They specify also the use generally of monophenyl ethers of polyoxyethylene, containing from 2 to 7 ethylene oxide units per molecule, as a plasticizer. They indicate, on the other hand, that a glycerin type of plasticizer may be used under very particularly defined conditions. In that connection, in Example 5, they prepared a first mixture of 100 parts of a polyvinyl alcohol resin, containing about 37% of residual acetate groups and having a solution viscosity of 9 cps, with 35 parts of a phenolic ether of a polyoxyethylene resin containing an average of 5 oxyethylene units per molecule as a plasticizer. They also prepared a second mixture of 100 parts of an essentially completely hydrolyzed polyvinyl acetate, having a solution viscosity of 15 cps, with 25 parts of dry glycerin as a plasticizer. They then combined 95 parts by weight of the first mixture and 5 parts by weight of the second mixture, after which the combined mixtures were pelletized and fed to an extruder die system for preparation of film.